A light-emitting diode lighting device for lighting light-emitting diodes that are connected in series has been proposed so far (see, e.g., JP Pat. No. 4581646 (hereinafter referred to as “Document 1”)).
A light-emitting diode lighting device disclosed in Document 1 includes a rectifier circuit, a light-emitting diode circuit and a lighting control circuit. The rectifier circuit is configured to full-wave rectify an AC voltage from an AC power supply, and a pulsating voltage obtained by full-wave rectification of the rectifier circuit is to be supplied to the light-emitting diode circuit. The light-emitting diode circuit is formed of a series circuit of a plurality of light-emitting diodes.
In the light-emitting diode lighting device, the plurality of light-emitting diodes are divided into a plurality of groups. The lighting control circuit performs lighting control of the plurality of light-emitting diodes so that (a) groups of which light-emitting diodes are lit more increase(s) as a value of the pulsating voltage from the rectifier circuit more increases. The lighting control circuit also performs lighting control of the plurality of light-emitting diodes so that (a) groups of which light-emitting diodes are lit more decrease(s) as the value of the pulsating voltage from the rectifier circuit more decreases.
In the light-emitting diode lighting device described in Document 1, the lighting control circuit is to increase or decrease the number of groups of which light-emitting diodes (semiconductor light-emitting devices) are lit in accordance with a value of the pulsating voltage from the rectifier circuit. The lighting control circuit therefore lights only light-emitting diodes in part of the plurality of groups and extinguishes (turns off) light-emitting diodes in remaining part of the plurality of groups when the value of the pulsating voltage is small.
In a case where the plurality of light-emitting diodes are mounted on a surface of a substrate, it is considered that light-emitting diodes in an identical group would be mounted together. Only light-emitting diodes in part of the plurality of groups are lit when the value of the pulsating voltage is small. In this case, if the light-emitting diodes in part of the plurality of groups are unevenly mounted on a corner of a mounting region of the substrate, unevenness may occur in a light output from the mounting region (i.e., a light output from a surface light source), where the mounting region is a region of the substrate, on which the plurality of light-emitting diodes are mounted. In a case where the plurality of light-emitting diodes are mounted so that light-emitting diodes of each group are evenly arranged on the mounting region of the substrate, the light-emitting diodes constituting the plurality of groups are mixed. In this case, wiring for connecting among light-emitting diodes in an identical group may become complicated.